Spray drying apparatus



April 28, 1959 M. E: BARZELAY SPRAY DRYING APPARATUS 2 Sheets- Sheet. 1

Filed Jan. 17, 1955 INVENTOR. MARTIN BEAR ZELAY BY ATZDRNEY April 28,1959' Filed Jan. 17, 1955 M. E. BARZELAYY: 2,334 049 SPRAYDRYING-APPARATUS 2 sheets sheet 2 HVVENTUR.

ATTORNEY MARTIN E .EARZIELAY This invention relates to apparatus forspray drying liquids containing solids, such as milk in a condensedstate, and more particularly relates to improvements in the nozzleconstruction for delivering a heated drying medium into a spray dryingchamber.

In spray drying of liquids, it has been the practice to deliver a heateddrying medium into a drying chamber through one or more nozzles, at themouth of which are centrally disposed liquid spraying devices foratomizing the liquid containing solids in the path of the flow of eateddrying medium. For efficient drying action, it is desirable to employ adrying medium such as heated air, the temperature of which is as high asthe solids can withstand without injury, in order to promotesubstantially instantaneous evaporation, and further, as in the case ofmilk, to enhance the production of a coarse powder. In an applicationSerial No. 474,457, filed December 10, 1954, issued as Patent #2,835,597on May 20, 1958, there is disclosed a drying process wherein bytemperature gradation in the drying medium in the region of evaporation,the advantage of rapid evaporation through utilization of a hightemperature evaporating medium with the resulting promotion of coarsepowder production is set forth.

In the usual drying medium nozzles employed in spray drying, there issometimes a tendency for powder to deposit upon the internal nozzlesurface by reason of eddy currents in the region of the merging of themouth of the nozzle with the drying chamber. The collection of smallamounts of dried powder on the nozzle causes such powder to be subjectedover extended periods to the heat of the blast of the drying mediumdelivered through the nozzle, and causes scorching and burning of thepowder. Such powder upon dislodging mixes with the powder deposited inthe drying chamber, or. is air-borne through the chamber exhaust, andspoils the quality of the powder produced by the apparatus, which mightotherwise be of a premium grade. Additionally the collection of powderon the nozzle surfaces creates a fire hazard, and has been known tosmolder or to burst into flame and disrupt the operation, which wouldotherwise be continuous. Such collection requires shutting down theapparatus for cleaning of the nozzle surfaces.

T o forestall such tendency for the powder to deposit, a number ofsolutions have been proposed and tried, each of which has given noimprovement or resulted in other detrimental effects. Decreasing thedrying medium nozzle diameter to increase velocity has caused even worsefire hazards and deposits. Increasing milk nozzle size to give a wetspray has resulted in sticking of particles to the drying chamber wallsand undesirably high moisture content in the final product withoutcuring nozzle deposit. Increasing liquid temperature, or reducing dryingmedium temperature have also been proposed, but have a detrimentaleffect on the final dried powder produced, as will appear from aconsideration of the pending application to which reference has beenmade.

The present invention is directed to an arrangement for 2, preventingthe powder from contacting the nozzle sur faces, and more particularlyembodies means for establishing adjacent to substantially the entireinternal surface of the nozzle, a flow of drying medium controlled bothas to velocity and temperature, and moving in the direction of thenozzle air blast. The flow acts as an impenetrable surface curtainwithin the nozzle, which is effective to prevent powder from contactingthe nozzle. The apparatus establishes a boundary layer of air flowingalong and immediately adjacent to the internal surface of the nozzle.More particularly, in a practical embodiment of the invention, there isemployed an inner wall in the form of a spaced liner within the nozzle,such wall having a plurality of arcuate louvres for discharging airalong the internal surface of the liner, the liner wall, and nozzleforming an annular chamber for receiving air under controlled pressureand temperature and discharging such air through the louvres. Theboundary layer of air thus provided may in practice he of a lowertemperature than the temperature of the drying medium, and because ofits impenetrable protective effect over the nozzle surface, higherdrying medium temperatures may be utilized in the main nozzle blast.

As a further explanation of the protective layer referred to, when fluidflows along and in contact with a wall, it is retarded at the surface ofthe wall by the viscous forces present in all fluids. In fact, at thewall the velocity is zero but a short distance out from the wall, thefluid stream has the free stream velocity. The retarded layer of fluidis called the boundary layer. In a nozzle, the flow in the boundarylayer continues to thicken in the direction of flow, and finally thereis a reversal of flow along the wall, a breaking away of the boundarylayer from the wall and turbulence. This retardation and reversal offlow is due to energy losses associated with the wall friction. Byreenergizing the boundary layer with fluid introduced parallel to thewall, the adverse eflfect of the boundary layer is overcome, andreversal prevented. In the case of milk spray drying, this reversal offlow in the boundary layer is particularly detrimental since alreadydried particles, or partially dried particles of milk are carried alongin the reverse stream and adhere to the nozzle wall aspreviously setforth.

The object of the invention is to provide a nozzle on which depositingof the desiccated material is prevented and in which elevated air blasttemperatures may be employed safely, withoutfire hazard and Withoutcontamina-' tion of the product by scorched or burned particles.

The above features and other objects of the invention will appear morefully hereinafter from the following detailed description when taken inconjunction with the accompanying drawings. It is expressly understoodthat the drawings are employed for purposes of illustration only and arenot designed as a definition of the limits of the invention, reference.being had for this purpose to the appended claims.

In the drawings wherein like reference characters indicate like parts:

Figure 1 is a sectional view through a single nozzle embodying theinvention, and mounted in the end wall of a drying chamber, with a sprayjet associated therewith;

Figure 2 is a perspective view of the nozzle with portions thereof cutaway; and

Figure 3 is any enlarged fragmentary perspective view of a segmentalportion of the nozzle.

In Figure 1, there is shown a drying chamber 10, having an end wall 12,in. which is mounted one or more nozzles 14 of generally frusto-conicalshape, the mouth 16 of the nozzle discharging into the drying chamberand the inlet end 18. of the nozzle coupling with a hot air supply ductor plenum chamber 20, having a wall 22.

Extending through the center of the nozzle thus shown is a solidscontaining liquid supply tube 24 terminating in an atomizing spray jet26, such tube extending through a protective sleeve 28, which inpractice may serve as heat insulation between the tube and hot blastpassing through the nozzle. The jet may be of the centrifugal or othertype, and the atomization pattern may vary from that shown.

The nozzle comprises an outer tapered wall 30, to which there is appliedin spaced relation an inner wall or spaced liner 32, thus forming anannular chamber 33. The liner wall is provided with an outwardlyextending flange 34, at the entrance end thereof adapted to be securedto the supply duct wall, and an outwardly extending flange 36 at themouth thereof, which flange is secured to a supporting annular plate 38having its rim overlying and secured to the wall 12 of the dryingchamber.

The liner wall is provided with a multiplicity of louvrelike openings 39extending in an arcuate segmental manner around the liner wall, each ofsuch louvre-like openings comprising an inwardly struck deflector 41suitably inclined to direct air emerging from the chamber 33 in adirection along the internal wall of the liner, toward the mouth of thenozzle. The chamber 33 is supplied with air under pressure by an annularmanifold 40 having a plurality of ducts 42 connecting with ports 43 inthe end flange 34 of the liner wall 32. Such manifold is supplied withair under pressure through a suitable control valve 44.

In practice, a heated drying medium, such as air, enters the nozzle andflows in the general direction of arrows A. The blast of air isaccelerated by the throat effect of the nozzle, and emerges from themouth thereof to impinge upon the fog of atomized liquid 46 from thespray jet 26. The heated air rapidly evaporates the moisture from theparticles suspended by the atomization of the liquid containing thesolids, and the dried particles either drop upon the chamber bottom forcollection, or are air borne to a centrifugal separator for collectionin the drying chamber exhaust (not shown). The temperature of the airblast passing through the nozzle may be in the order of 420 F. orsubstantially higher in the case of milk drying. It is to be understoodthat the temperature depends upon the nature of the solids from whichthe moisture is to be evaported. For other types of liquids in solids,it will be possible to similarly sub stantially raise the dryingtemperature, and thus increase process efi'iciency, without detrimentalsticking, burning and scorching.

Without the liner 32, the hot air blast in passing through the nozzlehas a tendency to heat the nozzle to the temperature of the air of theblast, and should particles of solids being dried, or in a dried statecome in contact therewith and become temporarily lodged thereon as aresult of eddy currents at the mouth of the nozzle, such particles wouldbe subjected to extended heating, suflicient to scorch the particles.Should such particles deposit upon the nozzle internal wall insuflicient quantity, the heat may cause ignition and burning of theparticles. The scorched or burned particles, on burning become dislodgedand are carried into the chamber and intermix with the dried product,contaminating the product and rendering the same unfit to meet thestandards set up for commercial purposes.

To prevent the occurrence of particles reaching the nozzle wall, airunder pressure is introduced into the chamber 33 from the manifold 40,which air is emitted from the louvres 39 in the direction indicated byarrows B and caused to flow along the internal surface of the linerwall, the air thus introduced traveling along with the blast or at avelocity slightly greater than the blast in the annular region 47generally defined by the line 46, the inner wall surface of the linerwall, and the extension thereof as indicated by the line 48. A layer ofinter-mixing of the air thus introduced and that of the 4 air blasttakes place in the region 51 defined by the line 46 and the line 50.

The air supplied through the control valve 44 to the manifold 40 shouldpreferably be unheated air. Its temperature may be somewhat elevated,however, by flow through the manifold and ducts which are exposed to thetemperature within the supply duct 20. Thus the central region 53 of themain blast of air as it leaves the nozzle will be undisturbed so far asits temperature is concerned, but the region 51 or intermixed air willevidence a somewhat lower temperature, whereas the air in the outerregion 47 will evidence a still lower temperature. The overall effect ofthe apparatus is to produce a blast of air, the temperature of whichshows a gradient, the hottest air being directed into the centralportion of the atomization fog, close to the jet 26 Where the moisturedensity is greatest.

The apparatus as thus provided and when operated under the conditionsset forth above, provides a means whereby extremely high blasttemperatures may be employed, for example, as high as the fog suspendedsolids can accommodate, whereby substantially instantaneous drying iseffected. At the same time the nozzle is protected against solidscollecting upon the nozzle surfaces, and the outer cooler region of theblast operates to complete the drying of any solids, the evaporation ofwhich has not been efiected in the central region.

In the case of milk drying, the apparatus permits the use of a spray ofconcentrated milk whose temperature at the spray jet is maintainedrelatively low for beneficial reasons as set forth in the herein abovereferred to application, since the temperature of the air blast can beelevated not only to compensate for a low temperature of theconcentrated supply, but to a higher temperature to provide more rapidand substantially instantaneous drying. At the same time, there ispresent a boundary layer of protection against deposit of driedparticles upon the nozzle, and thus protection from possible scorching,burning or ignition, which would ultimately result from such deposit.Further, the apparatus is rendered continuous in its operation, sinceshutdowns to clean the nozzles is made unnecessary.

Although a single embodiment of the invention has been illustrated anddescribed, it is to be understood that the invention is not limitedthereto. As various changes in the construction and arrangements may bemade without departing from the spirit of the invention, as will beapparent to those skilled in the art, reference will be had to theappended claims for a definition of the limits of the invention.

What is claimed is:

1. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a wall of the chamber for introducing heated drying mediuminto the chamber, means for delivering a blast of heated drying mediuminto the chamber through the nozzle, a source of additional dryingmedium independent of said blast delivering means, and means foradmitting said additional drying medium into the nozzle along theinternal surface thereof to energize a boundary layer moving with theblast over substantially the entire nozzle inner surface.

2. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a wall of the chamber for introducing heated drying mediuminto the chamber, a spray head for liquids containing solids mountedcentrally with respect to the nozzle and in the region adjacent thechamber end of the nozzle, means for delivering a blast of heated dryingmedium into the chamber through the nozzle, a source of additionaldrying medium independent of said blast delivering means, and means foradmitting said additional drying medium into the nozzle along theinternal surface thereof to energize a boundary layer over substantiallythe entire nozzle inner surface.

3. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a Wall of the chamber for introducing heated drying mediuminto the chamber, said nozzle being tapered and reducing in crosssectiontoward the chamber end, means for delivering a blast of heated dryingmedium into the chamber through the nozzle, a source of additionaldrying medium independent of said blast delivering means, and means foradmitting said additional drying medium of a lower temperature into thenozzle through and along the internal surface thereof to energize aboundary layer over substantially the entire nozzle surface.

4. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a wall of the chamber for introducing heated drying mediuminto the chamber, said nozzle gradually reducing in cross section towardthe chamber end, a spray head for liquids containing solids mountedcentrally with respect to the nozzle and in the region adjacent thechamber end of the nozzle, means for delivering a blast of heated dryingmedium into the chamber through the nozzle, a source of additionaldrying medium independent of said blast delivering means, and means foradmitting said additional drying medium of a lower temperature into thenozzle through and along the internal surface thereof to energize aboundary layer over substantially the entire nozzle surface.

5. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a wall of the chamber for introducing heated drying mediuminto the chamber, said nozzle having an internal liner and an outer wallproviding an annular chamber, a spray head for liquids containing solidsmounted centrally with respect to the nozzle and in the region adjacentthe chamber end of the nozzle, means for delivering a blast of heateddrying medium into the chamber through the nozzle, means for deliveringa relatively small amount of additional drying medium of a difierenttemperature into the annular chamber of the nozzle, and louvres in theliner of said nozzle inclined to direct said additional drying mediuminto the nozzle and in a direction toward said chamber, said louvresbeing located over substantially the entire surface of said liner,whereby said additional air passing through said louvres energizes theexisting boundary layer travelling along the surface with the blast oversubstantially the entire internal surface of said liner.

6. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a wall of the chamber for introducing heated drying mediuminto the chamber, said nozzle having an internal liner and an outer wallproviding an annular chamber, a spray head for liquids containing solidsmounted centrally with respect to the nozzle and in the region adjacentthe chamber end of the nozzle, means for delivering a blast of heateddrying medium into the chamber through the nozzle, means for deliveringa relatively small amount of additional drying medium into the annularchamber of the nozzle, and deflecting ports in the liner of said nozzleadapted to direct said additional drying medium into the nozzle and in adirection toward said chamber, said ports being located oversubstantially the entire surface of said liner, whereby said additionalair passing through said ports energizes the existing boundary layertravelling along the surface with the blast over substantially theentire internal surface of said liner.

7. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a wall of the chamber for introducing heated drying mediuminto the chamber, said nozzle having an internal liner and an outer wallproviding an annular chamber, means for delivering a blast of heateddrying medium into the chamber through the nozzle, means for deliveringa relatively small amount of additional drying medium into the annularchamber of the nozzle, and means distributed over the surface of theliner of said nozzle to direct said additional drying medium into thenozzle and in a direction toward said chamber, whereby said additionalair passing through said directing means energizes the existing boundarylayer travelling along the surface with the blast over substantially theentire internal surface of said liner.

8. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a wall of the chamber for introducing heated drying mediuminto the chamber, said nozzle having an internal liner and an outer wallproviding an annular chamber, means for delivering a blast of heateddrying medium into the chamber through the nozzle, means for deliveringa relatively small amount of additional drying medium into the annularchamber of the nozzle, and louvres in the liner of said nozzle inclinedto direct said additional drying medium into the nozzle and in adirection toward said chamber, said louvres being located oversubstantially the entire surface of said liner, whereby said additionalair passing through said louvres energizes the existing boundary layertravelling along the surface with the blast over substantially theentire internal surface of said liner.

9. In a spray drying apparatus, a drying chamber, a drying medium nozzlemounted in a wall of the chamber, means for delivering under a firstblast pressure a blast of heated drying medium into the chamber throughthe nozzle, a second source of air pressure suitably related to theblast pressure and differing from the blast pressure, and meansincluding a multiplicity of ports over the entire internal surface ofthe nozzle communicating with said second source of pressure, said meansserving to control the boundary layer over substantially the entireinternal surface of the nozzle and prevent flow along the internalsurface in a reverse direction from the main nozzle blast.

10. In a spray drying apparatus, a drying chamber, a drying mediumnozzle mounted in a wall of the chamber, means for delivering under afirst blast pressure a blast of heated drying medium into the chamberthrough the nozzle, a manifold exterior of said nozzle comprising asecond source of pressure suitably related to the blast pressure anddiffering from the blast pressure, and means including a multiplicity ofports over the entire internal surface of the nozzle communicating withsaid manifold, said means serving to control the boundary layer oversubstantially the entire surface and prevent flow along the internalsurface in a reverse direction from the main nozzle blast.

References Cited in the file of this patent UNITED STATES PATENTS1,087,515 Sprenger Feb. 17, 1914 1,753,915 Bowen Apr. 8, 1930 1,779,516Stevenson Oct. 28, 1930 1,829,477 Douthitt Oct. 27, 1931 2,035,673Schultz Mar. 31, 1936 2,413,420 Stephanofi Dec. 31, 1946 2,460,546Stephanoff Feb. 1, 1949 2,478,557 Bell et a1. Aug. 9, 1949 2,510,645McMahan June 6, 1950

